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Respiratory resistance from 1 to 46 ATA measured with the interrupter technique

Authors:
  • Clarke Life Support Consulting

Abstract

Measurements of respiratory resistance by an interrupter technique were made in six subjects during a Navy saturation dive to 457 m. Repeated measurements were made at five depths with complete pulmonary function testing after the dive. Increase in resistance was about linear with gas density (rho). Three smokers exhibited a significantly steeper slope of the respiratory resistance versus rho relationship than three nonsmokers. The disparity in resistance among the divers became considerable only at great pressure. Likewise, the predictions of two contradictory fluid dynamic theories agreed fairly well with our data and with each other over the densities explored and disagreed greatly with our data only at higher pressures.

 
        
       

  
  
 
  
 
 
     
    

  
J. 
           
 

  
       
 
       
    

 

    
 
        
     

  
  
 
        

         
        
      

      
      

 w. 
  
     

         
     

... Although this technique gives an indication of the degree of respiratory muscle activation [16] and central respiratory drive [17], a single point measurement does not allow calculation of the WOB. P .1 airway resistance values at sea level are comparable to values obtained by the traditional esophageal balloon technique [18,19], and have been used to assess airway resistance during simulated dives at depths up to 1450 feet of seawater (fsw) [20]. ...
... Both submersion and depth impose obvious limitations on physical exertion during open water dives due to these increases in POB. These increases in POB have been found before [7,13,20], as has the associated limitation to exercise [2,3]. SLL affects both inspiration and expiration at depth in the presence of increased gas density, particularly during exercise. ...
... NEDU performance goals based on diver respiratory flow rate have served the Navy well for decades 2,3 . Nevertheless, those historical goals have never explicitly considered gas density, which is a major contributor to the load on a diver's respiratory muscles 4 . ...
Technical Report
Full-text available
This report describes the use of Predict, in-house designed prediction software. NEDU performance goals for underwater breathing apparatus (UBA) based on ventilatory flow rate have served the Navy well for decades. Nevertheless, gas density is a major determinant of respiratory loading at depth, based on both experimental evidence and simple models of fluid mechanics. An understanding of the influence of flow rate and gas density are vital to understanding the performance characteristics of UBA, and the probable tolerance of a diver to those influences. Over a decade ago NEDU developed a constant respiratory impedance model for determining acceptable pressure drops across UBA, and created software to predict the tolerance of divers to UBA under varying dive conditions. The so-called maximum respiratory impedance model was calibrated on Navy manned dive results, and this paper describes the use of that model and the associated Predict software to predict diver tolerance based on unmanned data. It is arguably a more complete approach compared to methods already in Navy use, and is particularly useful in estimating the risk of diving UBA made inadequate by design or accident.
... Examples of these seminal studies are found in Anthonisen et al (1971), Broussolle et al (1976), Maio and Farhi (1967), Peterson and Wright (1976), and Varene et al (1967). Clarke et al (1982) found on a 457 msw (1500 fsw) dive at NEDU that the power for respiratory resistance as a function of gas density in six resting subjects (over 120 measurements) was not much different from the 0.5 used in the first term of equation 9 (Pedley's fluid dynamic based theory), and was similar to the results of Jaeger and Matthys (1970) for density changes at 1 ata (1970). ...
Technical Report
Full-text available
NEDU performance goals based on flow rate have served the Navy well for decades. Nevertheless, gas density is a major determinant of respiratory loading using both simple models of fluid mechanics and experimental evidence. An understanding of the influence of both respiratory ventilatory rates (flow) and density are vital to understanding the complete performance characteristics of UBA, and the probable tolerance of a diver to those influences. The constant impedance approach for determining acceptable pressure drops across UBA is a mechanism for combining the best of previous standards for UBA into a unified concept that takes into account engineering requirements, psychophysics, and respiratory physiology, including the fluid dynamics of flow in divers’ airways. It allows testing laboratories to make maximum use of all of their testing data, and to present that data in an easily interpretable two or three dimensional format.
Article
Background The relationship between air pollution and meteorological factors on diseases has become a research hotspot recently. Nevertheless, few studies have touched the inferences of nitrogen dioxide (NO2) and atmospheric pressure (AP) on hospitalization risk for chronic obstructive pulmonary disease (COPD). Objectives To investigate the short-term impact of particulate air pollutants and meteorology factors on hospitalizations for COPD and quantify the corresponding risk burden of hospital admission. Methods In our study, COPD cases were collected from Guangzhou Panyu Central Hospital (n = 11,979) from Dec of 2013 to Jun 2019. The 24-h average temperature, relative humidity (RH), wind speed (V), AP and other meteorological data were obtained from Guangzhou Meteorological Bureau. Air pollution data were collected from Guangzhou Air Monitoring Station. The influence of different NO2 and AP values on COPD risk was quantified by a distributed lag nonlinear model (DLNM) combined with Poisson Regression and Time Series analysis. Results We found that NO2 had a non-linear relationship with the incidence of COPD, with an approximate “M" type, appearing at the peaks of 126 μg/m³ (RR = 1.32, 95%CI, 1.07 to 1.64) and 168 μg/m³ (RR = 1.21, 95%CI, 0.94 to 1.55), respectively. And the association between AP and COPD incidence exhibited an approximate J-shape with a peak occurring at 1035 hPa (RR = 1.16, 95% CI, 1.02 to 1.31). Conclusions The nonlinear relationship of NO2 and AP on COPD admission risk in different periods of lag can be used to establish an early warning system for diseases and reduce the possible outbreaks and burdens of COPD in a sensitive population.
Chapter
Diving is a very stressful condition for humans. In addition to limited measures for breathing gas supply, hyperbaric and/or hyperoxic stresses are associated with various kinds of diving measures depending upon the diving procedures. Factors affecting host responses may include not only types of diving or concomitant factors such as gas supply systems and breathing gases themselves but also various situations caused under high pressure. Hyperbaric diving stresses are very unique from the viewpoint of diving physiology as well as an emerging discipline, e.g., molecular based medicine. In this chapter, host response against hyperbaric and/or hyperoxic stresses is discussed through the mechanisms of diving-related disorders.
Chapter
Inertance of the human respiratory system is negligible in normal environments, but has been shown experimentally to increase in simple direct proportion to the density of the breathing gas (Mead 1956; Peterson and Wright 1976; Sharp et al. 1964). This raises the question of how inertance in dense-gas environments compares with airflow resistance, which is also density-dependent. The pressure necessary to accelerate gas is greatest when flow is changing direction at end-inspiration and end-expiration, whereas an effect on pressure for gas flow is greatest during inspiration and expiration.
Article
Deep sea diving might cause tremendous physical or psychological stress to divers. The present study aims to evaluate the pulmonary stress experienced by navy divers after a simulated deep wet dive. Nineteen navy divers took part in this study during their annual deep dive training. Ten divers were exposed to 190 feet of sea water (fsw) breathing compressed air on day 1 and to 250 fsw breathing helium-oxygen (Heliox) gas mixture on day 3. Other nine divers were exposed to 220 fsw on day 1 and 285 fsw on day 3 breathing Heliox gas mixture. The bottom time ranged from 5 to 8 min and the standard U.S. Navy Air and Surface-Supplied Helium Oxygen Decompression Tables were then followed for surfacing. Air dive to 190 fsw caused a significant decrease in the FEV 1/FVC, but no statistically significant difference in the FEV 1. On the other hand, the FEV 1 increased significantly after a Heliox dive to 220 fsw, but not after dives to 250 or 285 fsw. Our results suggested that deep diving using different gas mixtures may have diverse impacts on pulmonary functions. Therefore, strict criteria on pulmonary function test may be necessary in the fitness recommendation for recruitment of deep divers.
Article
Full-text available
Water covers over 70% of the earth, has varying depths and temperatures and contains much of the earth's resources. Head-out water immersion (HOWI) or submersion at various depths (diving) in water of thermoneutral (TN) temperature elicits profound cardiorespiratory, endocrine, and renal responses. The translocation of blood into the thorax and elevation of plasma volume by autotransfusion of fluid from cells to the vascular compartment lead to increased cardiac stroke volume and output and there is a hyperperfusion of some tissues. Pulmonary artery and capillary hydrostatic pressures increase causing a decline in vital capacity with the potential for pulmonary edema. Atrial stretch and increased arterial pressure cause reflex autonomic responses which result in endocrine changes that return plasma volume and arterial pressure to preimmersion levels. Plasma volume is regulated via a reflex diuresis and natriuresis. Hydrostatic pressure also leads to elastic loading of the chest, increasing work of breathing, energy cost, and thus blood flow to respiratory muscles. Decreases in water temperature in HOWI do not affect the cardiac output compared to TN; however, they influence heart rate and the distribution of muscle and fat blood flow. The reduced muscle blood flow results in a reduced maximal oxygen consumption. The properties of water determine the mechanical load and the physiological responses during exercise in water (e.g. swimming and water based activities). Increased hydrostatic pressure caused by submersion does not affect stroke volume; however, progressive bradycardia decreases cardiac output. During submersion, compressed gas must be breathed which introduces the potential for oxygen toxicity, narcosis due to nitrogen, and tissue and vascular gas bubbles during decompression and after may cause pain in joints and the nervous system. © 2015 American Physiological Society. Compr Physiol 5:1705-1750, 2015.
Article
1. The interrupting device must be located between the mouthpiece and the pneumotachometric tube. 2. The best result of calculation of Rae (the smallest scatter and minimal value of muscular efforts) is obtained by using the intraoral pressure after the end of oscillations P1; under these circumstances the flow rate is determined immediately before interruption. 3. Interruption of the air flow is best carried out during quiet breathing, at near-maximal flow rate, i.e., about 0.5 liter/sec. 4. To obtain sufficiently stable data the mean value of measurements made during at least five respiratory cycles must be determined.
Article
Exposure to elevated ambient pressure (hyperbaric conditions) occurs most commonly in underwater diving, during which respired gas density and partial pressures, work of breathing, and physiological dead space are all increased. There is a tendency toward hypercapnia during diving, with several potential causes. Most importantly, there may be reduced responsiveness of the respiratory controller to rising arterial CO2, leading to hypoventilation and CO2 retention. Contributory factors may include elevated arterial PO2, inert gas narcosis and an innate (but variable) tendency of the respiratory controller to sacrifice tight control of arterial CO2 when work of breathing increases. Oxygen is usually breathed at elevated partial pressure under hyperbaric conditions. Oxygen breathing at modest hyperbaric pressure is used therapeutically in hyperbaric chambers to increase arterial carriage of oxygen and diffusion into tissues. However, to avoid cerebral and pulmonary oxygen toxicity during underwater diving, both the magnitude and duration of oxygen exposure must be managed. Therefore, most underwater diving is conducted breathing mixtures of oxygen and inert gases such as nitrogen or helium, often simply air. At hyperbaric pressure, tissues equilibrate over time with high inspired inert gas partial pressure. Subsequent decompression may reduce ambient pressure below the sum of tissue gas partial pressures (supersaturation) which can result in tissue gas bubble formation and potential injury (decompression sickness). Risk of decompression sickness is minimized by scheduling time at depth and decompression rate to limit tissue supersaturation or size and profusion of bubbles in accord with models of tissue gas kinetics and bubble formation and growth. © 2011 American Physiological Society. Compr Physiol 1:163-201, 2011.
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